Polystyrene polymers of structure :
in which, R' and R2 are the same or different and are each C1-4 alkyl; R3 is (CH2)nR4 in which R4 is C3-6 cycloalkyl or a bicyclic carbocyclic ring of up to 10 carbon atoms and n is 1 to 12, or R3 is (CH2)nCH = RSR6 in which n is 1 to 12 and R5 and R6 together form a C3-6 cycloalkyl ring or a bicyclic carbocyclic ring of up to 10 carbon atoms; R7 is hydrogen or a group CH2NR1R2R3X-; X- is a counter ion; a, b and c are numbers which indicate the relative molar percentages of the units present in said polymer, (b) being from about 1 to about 10 molar percent, and (c) being from about 30 to about 98 molar percent; m is a number indicating the degree of polymerisation of said polymer, processes for their preparation, compositions containing them and their use in therapy as bile acid sequestering agents.